This invention relates to an internal combustion engine, and more particularly to a two cycle internal combustion engine having a fuel injection system.
Carburetors have commonly been used to supply a fuel-and-air mixture to both four stroke and two stroke internal combustion engines. Hand held yard tools, such as chainsaws and weed trimmers, use small two stroke engines having carburetors with a diaphragm fuel delivery pump and a diaphragm fuel metering system. For larger fuel demand two stroke engine applications which experience little change in engine orientation during operation, float-type carburetors are commonly utilized. Such large applications include outboard marine motors, snowmobiles and other recreational vehicles; In operation, large two stroke outboard marine engines, and large engines of other recreational vehicles have an engine cylinder displacement of at least fifty cubic centimeters, CC, per cylinder, and typically utilize a float-type carburetor. Large two stroke engines with float-type carburetors have a high level of hydrocarbon exhaust emissions which are detrimental to the environment and exceed the exhaust emission requirements imposed by the state of California and the emission requirements proposed by the Environmental Protection Agency of the United States Government and the Governments of several other countries.
For marine two stroke engine applications, such as outboard motors, ignition timing is varied widely as compared to carburetor throttle opening, and in fact, most engine revolutions per minute, RPM, change is achieved from idle speed to approximately fit percent of maximum engine RPM by ignition timing. To change ignition timing with throttle opening, the marine industry has typically used throttle ignition linkage mechanisms to advance ignition timing in advance of the beginning and full opening of the carburetor throttle. This ignition timing curve verse engine RPM verse throttle opening is duplicated electronically in fuel injection systems.
Previous marine fuel injection system technology, utilized fuel systems sized appropriately for fuel delivery between idle and wide open throttle conditions with the injector fuel flow typically synchronized with the engine throttle air valve. Because smaller two stroke engines are equipped with fixed ignition and port timing restraints, they often produce higher engine emissions on a per unit or CC displacement basis, and have additional fuel system calibration challenges. Often there is; cycle-to-cycle variation in fuel charge delivery from decreased injection system air flow (fuel pooling and wetting in the delivery manifold), insufficient dwell time inside the engine cylinder for fuel charge mixing and preparation, dilution of the incoming fuel charge in the cylinder with exhaust gas residue from insufficient scavenging at low speeds, and variation in cycle-to-cycle cylinder mean effective pressure from these factors resulting in unstable engine RPM.
A fuel injection system, for a large two-stroke engine with a displacement of at least fifty cubic centimeters per cylinder, injects a rich fuel and air mixture directly into each cylinder of the engine. The fuel injection system has a charge forming device which supplies a rich fuel-and-air mixture to a tuned injector tube for each cylinder connected adjacent one end through a port or valve to the cylinder and adjacent the other end to the engine crankcase. The charge forming device has an injector air inlet and fuel mixing passage to which, fuel is supplied by a primary fuel circuit under all engine operating conditions, while a separate inlet air flow passage supplies primary air to the crankcase of the engine. From the crankcase, the primary air is transferred to each cylinder usually through a transfer passage and/or inlet port or valve. Under engine wide open throttle conditions, a very minor quantity of fuel (with a lubricant such as oil therein) may be supplied through the engine inlet air flow passage to the crankcase and transferred to each cylinder to provide lubricant of the moving parts in the crankcase and some cooling of the engine. Fuel is supplied to the primary and crankcase circuits from a float bowl type common fuel chamber. Preferably, fuel is supplied to the fuel chamber from a fuel tank by gravity or by a low pressure fuel pump which may be a diaphragm type fuel pump actuated either mechanically or by pressure pulses from the engine crankcase or the engine inlet air flow passage.
Preferably, the primary air flow passage has a throttle valve. The separate fuel injector mixing passage is configured to provide a fuel flow rate therethrough proportional or correlating to the air flow through the primary air passage as controlled by the extent of the opening of the throttle valve. Moreover, the engine ignition timing is advanced in conjunction with and/or in advance of opening of the throttle valve to increase engine RPM. The ignition timing may be mechanically or electronically advanced and retarded in proportion to and in response to the extent of opening and closing of the throttle valve. However, for some engine applications, the fuel injector mixing passage and the engine primary air flow passage may each have separate throttle valves operably connected together to control in unison and provide proportional air flow through their separate passages. Preferably, both the fuel injector mixing passage and the engine primary air flow passage each have choke valves which are operably connected together so that they can be closed and opened in unison and provide proportional air flow through their passages for cold start fuel enrichment of the engine.
Objects, features and advantages of this invention include providing an arrangement of a mechanical fuel injection system for a large two stroke engine and a fuel charging device which provides a significant decrease in engine hydrocarbon exhaust emissions, significantly improved fuel economy, variable ignition timing used to enhance idle/slow speed stability, improved combustion stability, synchronized simultaneous throttling of both the engine inlet air flow and the fuel injector inlet air flow, synchronized simultaneous choking for cold starting of both the engine inlet primary air flow and the fuel injector inlet air flow, improved engine cold starting and warm-up, improved operating stability of the charge forming device, an extremely compact construction and arrangement, a relatively simple design, extremely low cost when mass produced, and which is rugged, durable, reliable, requires little maintenance and adjustment in use, and in service has a long useful life.